Method for producing silicon single crystal

ABSTRACT

A production method of monocrystalline silicon includes: growing the monocrystalline silicon having a straight-body diameter in a range from 301 mm to 330 mm that is pulled up through a Czochralski process from a silicon melt including a dopant in a form of arsenic; controlling a resistivity of the monocrystalline silicon at the straight-body start point to fall within a range from 2.50 mΩcm to 2.90 mΩcm; and subsequently sequentially decreasing the resistivity of the monocrystalline silicon to fall within a range from 1.6 mΩcm to 2.0 mΩcm at a part of the monocrystalline silicon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Division of U.S. application Ser. No. 16/622,502, filed Dec.13, 2019, which is the U.S. National Stage entry of PCT/JP2018/023030,filed Jun. 15, 2018, which claims priority to JP Application No.2017-127511, filed Jun. 29, 2017. The disclosure of each of theapplications identified above is herein incorporated by reference in itsentirety.

TECHNICAL FIELD

The present invention relates to a production method of monocrystallinesilicon.

BACKGROUND ART

In recent years, mobile devices such as mobile phones have been widelyused. Such devices strongly require long-term portability and usability.Accordingly, efforts have been made to increase a capacity of a batteryinstalled in the mobile device and decrease power consumption of themobile device itself.

In order to decrease power consumption of the mobile device itself, itis necessary to decrease power consumption of a semiconductor deviceinstalled in the mobile device.

For instance, since a low voltage power MOSFET (Metal OxideSemiConductor Field Effect Transistor), which is used as an electricpower device for a mobile device, has a certain internal electricresistance in an ON state, the low voltage power MOSFET itself consumeselectric power in accordance with an electrical current passing throughthe low voltage power MOSFET.

Accordingly, if the internal electric resistance of the low voltagepower MOSFET in the ON state can be reduced, power consumption of themobile device can be lowered. Based on such a background, an N-typemonocrystalline silicon having a low electric resistivity is stronglydemanded in order to achieve a small electric resistance of the lowvoltage power MOSFET in the ON state.

In a typical production method of monocrystalline silicon,monocrystalline silicon is pulled up while a resistivity thereof iscontrolled to meet a target value such that the resistivity of theentire monocrystalline silicon is constant.

The monocrystalline silicon having such a low resistivity has been knownfor easily causing dislocations during being pulled up through aCzochralski process and the like in a production process.

Patent Literature 1 discloses that, noting that a dopant concentrationbecomes high to generate abnormal growth due to compositionalsupercooling phenomenon in a tail of the monocrystalline silicon justbefore the end of the pulling up of the monocrystalline silicon,occurrence of dislocations in the tail is prevented by increasing theresistivity of the monocrystalline silicon at the tail.

CITATION LIST Patent Literature(s)

-   Patent Literature 1: JP 2010-184839 A

SUMMARY OF THE INVENTION Problem(s) to be Solved by the Invention

However, in typical techniques including that of Patent Literature 1,when the concentration of the dopant to be added to a silicon melt isincreased in order to reduce the resistivity of the monocrystallinesilicon to be pulled up, a freezing point depression of the silicon meltbecomes very large to generate abnormal growth due to compositionalsupercooling phenomenon. Due to the abnormal growth, after themonocrystalline silicon starts to be pulled up, dislocations sometimesoccur at a growth point of about 20% of a straight body from a shoulder.

In this case, a seed crystal needs to be immersed into the silicon meltin a crucible and be again pulled up. However, repetition of the pullingup increases a production cost of an ingot of the monocrystallinesilicon.

An object of the invention is to provide a production method ofmonocrystalline silicon having a low resistivity and a straight-bodydiameter in a range from 301 mm to 330 mm, without increasing aproduction cost.

Means for Solving the Problem(s)

Focusing on occurrence of dislocations at a straight-body start point,according to the invention, a resistivity at the straight-body startpoint is determined to be larger than a target value and subsequentlythe resistivity is sequentially reduced, thereby preventing theoccurrence of the dislocations at the straight-body start point.

Specifically, according to an aspect of the invention, a productionmethod of monocrystalline silicon includes: growing the monocrystallinesilicon having a straight-body diameter in a range from 301 mm to 330 mmthat is pulled up through a Czochralski process from a silicon meltincluding a dopant in a form of red phosphorus; controlling aresistivity of the monocrystalline silicon at a straight-body startpoint to fall within a range from 1.20 mΩcm to 1.35 mΩcm, andsubsequently sequentially decreasing the resistivity of themonocrystalline silicon to fall within a range from 0.7 mΩcm to 1.0 mΩcmat a part of the monocrystalline silicon.

According to the above aspect of the invention, occurrence ofdislocations is preventable by determining the resistivity of themonocrystalline silicon at the straight-body start point to range from1.20 mΩcm to 1.35 mΩcm. Accordingly, repetition of pulling up themonocrystalline silicon can be prevented and a production cost is notincreased, so that the monocrystalline silicon having a low resistivityand doped with red phosphorus is producible.

According to another aspect of the invention, a production method ofmonocrystalline silicon includes: growing the monocrystalline siliconhaving a straight-body diameter in a range from 301 mm to 330 mm that ispulled up through a Czochralski process from a silicon melt including adopant in a form of arsenic; controlling a resistivity of themonocrystalline silicon at a straight-body start point to fall within arange from 2.50 mΩcm to 2.90 mΩcm, and subsequently sequentiallydecreasing the resistivity of the monocrystalline silicon to fall withina range from 1.6 mΩcm to 2.0 mΩcm at a part of the monocrystallinesilicon.

According to the above aspect of the invention, with the same actionsand effects as the above, monocrystalline silicon having a lowresistivity and doped with arsenic is producible without increasing theproduction cost.

DESCRIPTION OF EMBODIMENT(S)

FIG. 1 schematically illustrates a structure of a pull-up apparatus ofmonocrystalline silicon according to an exemplary embodiment of theinvention.

FIG. 2 is a graph showing a relationship between a straight-body lengthand a resistivity in monocrystalline silicon in Examples with redphosphorus as a dopant.

FIG. 3 is a graph showing a relationship between a straight-body lengthand an occurrence rate of dislocations in monocrystalline silicon inExamples with red phosphorus as the dopant.

FIG. 4 is a graph showing a relationship between a straight-body lengthand a resistivity in monocrystalline silicon in Examples with arsenic asthe dopant.

FIG. 5 is a graph showing a relationship between a straight-body lengthand an occurrence rate of dislocations in monocrystalline silicon inExamples with arsenic as the dopant.

DESCRIPTION OF EMBODIMENT(S)

[1] Arrangement of Pull-Up Apparatus 1 of Monocrystalline Silicon

FIG. 1 schematically shows an exemplary structure of a pull-up apparatus1 for monocrystalline silicon. A production method of monocrystallinesilicon according to an exemplary embodiment of the invention isapplicable to the pull-up apparatus 1. The pull-up apparatus 1 includesa chamber 2 forming an external body and a crucible 3 disposed at thecenter of the chamber 2.

The crucible 3, which has a double structure formed by an inner quartzcrucible 3A and an outer graphite crucible 3B, is fixed to an upper endof a support shaft 4 that is rotatable and vertically movable.

An inner diameter of the inner quartz crucible 3A of the crucible 3 ispreferably in a range from 1.7 to 2.0 times as large as a straight-bodydiameter when the straight-body diameter of the monocrystalline silicon10 is in a range from 301 mm to 330 mm.

If the inner diameter of the crucible 3 is larger than the above range,a diameter of an opening of each of a heat shield plate 12 (describedlater) and the chamber 2 is increased, whereby the evaporated dopantadheres to a furnace body and foreign substances adhere to themonocrystalline silicon 10 to be likely to cause dislocations.

By determining the inner diameter of the crucible 3 in the above range,a distance between the monocrystalline silicon 10 and the quartzcrucible 3A is reducible and an evaporation amount of a silicon melt isreducible, so that evaporation of a dopant (e.g., red phosphorus andarsenic) is reducible and occurrence of dislocations at a straight-bodystart point due to segregation phenomenon of the dopant is preventable.

A resistance heater 5 is provided to an exterior of the crucible 3 in amanner to surround the crucible 3. A heat insulation material 6 isprovided outside of the heater 5 and along an inner surface of thechamber 2.

A pulling shaft 7 (e.g., wire), which is rotatable at a predeterminedspeed coaxially with the support shaft 4 and in a direction oppositefrom or the same as the direction of the support shaft 4, is providedabove the crucible 3. A seed crystal 8 is attached to a lower end of thepulling shaft 7.

A water-cooled body 11, which is a cylindrical cooler surrounding thegrowing monocrystalline silicon 10 above a silicon melt 9 of thecrucible 3, is disposed inside the chamber 2.

The water-cooled body 11 is, for instance, made of metal (e.g., copper)having an excellent thermal conductivity and is forcibly cooled bycooling water flowing inside the water-cooled body 11. The water-cooledbody 11 promotes cooling the growing monocrystalline silicon 10 andcontrols a temperature gradient between a central portion and aperipheral portion of the monocrystalline silicon in a direction of thepulling shaft 7.

Further, the cylindrical heat shield plate 12 is disposed surrounding anouter circumferential surface and a bottom surface of the water-cooledbody 11.

The heat shield 12 shields the growing monocrystalline silicon 10 fromhigh-temperature radiation heat from the silicon melt 9 in the crucible3, the heater 5, and a side wall of the crucible 3. Near a solid-liquidinterface (crystal growth interface), the heat shield plate 12, alongwith the water-cooled body 11, prevents heat diffusion to thelow-temperature water-cooled body 11 and controls the temperaturegradient between the central portion and the peripheral portion of themonocrystalline silicon in the direction of the pulling shaft.

A gas inlet 13 for introducing inert gas (e.g. Ar gas) into the chamber2 is provided at an upper part of the chamber 2. A gas outlet 14,through which the gas in the chamber 2 is sucked and discharged when avacuum pump (not shown) is driven, is provided at a lower portion of thechamber 2.

The inert gas introduced from the gas inlet 13 into the chamber 2 flowsdown between the growing monocrystalline silicon 10 and the water-cooledbody 11, flowing through a gap (liquid surface Gap) between the lowerend of the heat shield 12 and the liquid surface of the silicon melt 9,subsequently, outside the heat shield 12, further outside the crucible3, and subsequently flowing down outside the crucible 3 to be dischargedfrom the gas outlet 14.

For the growth of the monocrystalline silicon 10 using the pull-upapparatus 1, while an inside of the chamber 2 is kept under an inert gasatmosphere and reduced pressure, a solid material (e.g., polycrystallinesilicon) filled in the crucible 3 is heated by the heater 5 to bemelted, thereby forming the silicon melt 9. After the silicon melt 9 isformed in the crucible 3, the pulling shaft 7 is lowered to soak theseed crystal 8 in the silicon melt 9. While the crucible 3 and thepulling shaft 7 are rotated in a predetermined direction, the pullingshaft 7 is gradually pulled up, thereby growing the monocrystallinesilicon 10 overspreading the seed crystal 8.

[2] Production Method of Monocrystalline Silicon 10

The monocrystalline silicon 10 according to the exemplary embodiment isproducible using the above-described pull-up apparatus 1 by suitablyadding the dopant (e.g., red phosphorus and arsenic) to the silicon melt9 at the beginning of or during the pulling up process.

When the dopant is red phosphorus, a resistivity at a straight-bodystart point of the monocrystalline silicon 10 is controlled to fallwithin a range from 1.20 mΩcm to 1.35 mΩcm and then a doping amount ofred phosphorus is sequentially increased to decrease the resistivity ofthe monocrystalline silicon 10. Finally, the monocrystalline silicon 10having the resistivity in a range from 0.7 mΩcm to 1.0 mΩcm is obtained.

Similarly, when the dopant is arsenic, the resistivity at thestraight-body start point of the monocrystalline silicon 10 iscontrolled to fall within a range from 2.50 mΩcm to 2.90 mΩcm and then adoping amount of arsenic is sequentially increased to decrease theresistivity of the monocrystalline silicon 10. Finally, themonocrystalline silicon 10 having the resistivity in a range from 1.6mΩcm to 2.0 mΩcm is obtained.

The ingot of the monocrystalline silicon 10 according to the exemplaryembodiment can be pulled up under general pull-up conditions. During thepulling up process, the addition amount of the dopant is changed, adopant concentration is increased due to segregation phenomenon inaccordance with the pulling up, an introduction amount of inert gas tobe introduced into the chamber 2 is changed to promote evaporation ofthe dopant, and an inner pressure of the chamber 2 is changed, therebyproducing the monocrystalline silicon. The inner pressure of the chamber2 is preferably in a range from 30 kPa to 40 kPa.

When pulling up the monocrystalline silicon 10, a value of a ratiobetween a volume of heat by an upper heater 5A and a volume of heat by alower heater 5B in the heater 5 is preferably in a range from 1 to 4.When the value of the ratio is less than 1, in other words, the volumeof heat by the lower heater 5B is less than the volume of heat by theupper heater 5A, convection from the bottom of the crucible 3 towardunder the solid-liquid interface is not strengthened, so that theconvection with an unstable liquid temperature occurring from thesurface of the silicon melt 9 added with the dopant toward the crystalcannot be weakened. Accordingly, the temperature of the monocrystallinesilicon 10 becomes unstable to fail to eliminate or minimize occurrenceof dislocations.

On the other hand, when the value of the ratio in terms of the volume ofheat exceeds 4, a heat load at a lower portion of the crucible 3 isincreased, so that the crucible 3 may be deformed and quartz may bepeeled off.

When forming a shoulder of the monocrystalline silicon 10, it ispreferable to pull up the monocrystalline silicon 10 so as not togenerate a re-melt growth region of a large height (e.g., 200 μm ormore). Specifically, at the start of the shoulder formation, themonocrystalline silicon 10 is pulled up while the crucible 3 is rotatedat the rotation speed ranging from 16 rpm to 30 rpm. Subsequently, whena diameter of the shoulder is equal to or more than a half of thediameter of the straight body of the monocrystalline silicon 10, therotation speed of the crucible 3 is gradually lowered to fall within arange from 4 rpm to 12 rpm.

If the monocrystalline silicon 10 is pulled up at the rotation speed ofthe crucible 3 exceeding 30 rpm at the start of the shoulder formation,the operation of the pull-up apparatus 1 would be unstable to highlylikely cause deformation of the shoulder.

When the shoulder diameter is equal to or more than a half of thestraight-body diameter of the monocrystalline silicon 10, if therotation speed of the crucible 3 is less than 4 rpm, the silicon melt 9added with the dopant would be unstable to highly likely causeoccurrence of dislocations.

When the rotation speed of the crucible 3 exceeds 12 rpm, a fluctuationin an in-plane oxygen density and the resistivity of the monocrystallinesilicon 10 is increased, resulting in an unstable crystal quality.

When forming the straight body of the monocrystalline silicon 10, it ispreferable to pull up the monocrystalline silicon 10 so as not generatea re-melt region of a large height (e.g., 200 μm or more). Specifically,at the start of the straight body formation, the monocrystalline silicon10 is pulled up while the crucible 3 is rotated at the rotation speedranging from 9 rpm to 30 rpm. Subsequently, when the straight body ofthe monocrystalline silicon 10 is pulled up from a start point of thestraight body to reach a range from 50 mm to 200 mm, the rotation speedof the crucible 3 is changed to a range from 0.1 rpm to 7 rpm.

If the monocrystalline silicon 10 is pulled up at the rotation speedexceeding 30 rpm at the start of the straight body formation, theoperation of the pull-up apparatus 1 would be unstable to highly likelycause deformation of the straight body.

If the rotation speed of the crucible 3 is less than 0.1 rpm when thestraight body is in the range from 50 mm to 200 mm from the start pointof the straight body, the silicon melt 9 added with the dopant would beunstable to highly likely cause occurrence of dislocations.

When the rotation speed of the crucible 3 exceeds 7 rpm, the fluctuationin the in-plane oxygen density and the resistivity of themonocrystalline silicon 10 is increased to cause an unstable crystalquality.

It is also conceivable to eliminate or minimize occurrence ofdislocations by rotating the monocrystalline silicon 10 at a high speedwhen forming the shoulder in the same manner as in a case wheremonocrystalline silicon is pulled up so as to have a straight-bodydiameter ranging from 201 mm to 230 mm. However, in a case of thestraight-body diameter ranging from 301 mm to 330 mm, since thestraight-body diameter is large, crystal deformation easily occurs andthe monocrystalline silicon 10 is not rotatable at a high speed.

[3] Machining of Low Resistive Silicon Wafer and Low Resistive EpitaxialSilicon Wafer

When the dopant is red phosphorus, the ingot of the monocrystallinesilicon which has the straight-body diameter ranging from 301 mm to 330mm and is pulled up by the pull-up apparatus 1, has the resistivityranging from 0.7 mΩcm to 1.0 mΩcm at a part of the ingot close to a tailof the monocrystalline silicon 10.

The part close to the tail of the monocrystalline silicon 10 is cut intoa silicon wafer using a wire saw and the like. The obtained siliconwafer is subjected to lapping and polishing, whereby the silicon waferhaving a resistivity from 0.7 mΩcm to 1.0 mΩcm and a diameter of 300 mmis obtainable.

Further, the processed silicon wafer is subjected to annealing and anepitaxial film is formed on a surface of the silicon wafer, therebyproducing an epitaxial silicon wafer having a diameter of 300 mm, whichis to be delivered to a customer.

When the dopant is arsenic, the ingot of the monocrystalline silicon 10having the resistivity ranging from 1.6 mΩcm to 2.0 mΩcm is obtained atthe part close to the tail of the monocrystalline silicon 10 having thestraight-body diameter ranging from 301 mm to 330 mm.

The part close to the tail of the monocrystalline silicon 10 is cut intoa silicon wafer using a wire saw and the like. The obtained siliconwafer is subjected to lapping and polishing. Subsequently, the processedsilicon wafer having the diameter of 300 mm is to be delivered to acustomer According to the need, the customer forms an epitaxial film andproduces semiconductor devices.

EXAMPLES

[1] Dopant in Form of Red Phosphorus

The monocrystalline silicon 10 doped with red phosphorus was pulled upwhile a resistivity of the monocrystalline silicon 10 was controlled byadding red phosphorus as the dopant depending on a point in astraight-body length of the monocrystalline silicon 10.

The straight-body diameter of the monocrystalline silicon 10 was set ina range from 301 mm to 330 mm. The crucible 3 with the inner diameter of22 inch (558.8 mm) (the inner diameter of the crucible 3/thestraight-body diameter of the monocrystalline silicon=1.86) was used inExamples. The crucible 3 having the inner diameter of 32 inch (812.8 mm)(the inner diameter of the crucible 3/the straight-body diameter of themonocrystalline silicon=2.70) was used in Comparatives.

In Examples, the rotation speed of the crucible 3 was 16 rpm at thestart of the formation of the shoulder of the monocrystalline silicon10. When the diameter of the shoulder reached 150 mm, the rotation speedwas changed to 9 rpm, which defined 9 rpm as the rotation speed of thecrucible 3 at the straight-body start point. The rotation speed waschanged to 6 rpm at a point of 100 mm from the straight-body startpoint.

On the other hand, in Comparatives, the rotation speed of the crucible 3was 14 rpm at the start of the formation of the shoulder of themonocrystalline silicon 10. When the diameter of the shoulder reached150 mm, the rotation speed was changed to 6 rpm. While maintaining 6rpm, the straight body was pulled up. Results are shown in Table 1 andFIG. 2 .

In the following description, a straight-body length 0% point refers toa start point of the straight-body of the monocrystalline silicon 10,and a straight-body length 100% point refers to a start point of thetail of the monocrystalline silicon 10.

TABLE 1 Comp. 1 Ex. 1 Ex. 2 Comp. 2 resistivity straight-body length 0%point 1.45 1.35 1.22 1.15 [m Ω cm] (end of shoulder) straight-bodylength 20% point 1.3 1.23 1.13 1.06 straight-body length 40% point 1.21.13 1.05 0.98 straight-body length 60% point 1.11 1.03 0.96 0.89straight-body length 80% point 1.05 0.97 0.87 0.8 straight-body length100% point 1.01 0.92 0.8 0.72 (tail start point)

Presence or absence of occurrence of dislocations was checked at eachpoint. Results are shown in Table 2 and FIG. 3 . In Table 2, a crystalyield refers to a rate in length of a part of the monocrystallinesilicon having the resistivity of 0.7 mΩcm or less relative to themonocrystalline silicon pulled up without occurrence of dislocations.

TABLE 2 Comp. 1 Ex. 1 Ex. 2 Comp. 2 dislocations shoulder tostraigh-body  7%  21%  30%  87% rate 80 mm point (trial no./straigh-body 80 mm point to  7%  7%  10%  7% no.) straigh-body length20% point straigh-body length  0%  0%  0%  0% 20% to 40% pointstraigh-body length  0%  0%  0%  0% 40% to 60% point straigh-body length 0%  7%  0%  0% 60% to 80% point straigh-body length  0%  7%  10%  0%80% to 100% point tail start point  0%  14%  10%  0% dislocation-free in 87%  43%  40%  7% entire crystal length total 100% 100% 100% 100% Nshoulder to straigh-body 1 3 3 13 number 80 mm point (trial no.)straigh-body 80 mm point to 1 1 1 1 straigh-body length 20% point 0 0 00 straigh-body length 20% to 40% point 0 0 0 0 straigh-body length 40%to 60% point 0 1 0 0 straigh-body length 60% to 80% point 0 1 1 0straigh-body length tail 0 2 1 0 dislocation-free in 13 6 4 1 entirecrystal length total 15 14 10 15 diameter 300 mm 300 mm 300 mm 300 mmdopant red red red red phosphorus phosphorus phosphorus phosphoruscrystal yield   0%   7%  22%  30% charge amount 160 160 160 160straight-body length 715 715 715 715 rate of successful crystal inlength 0  10%  30%  40% length of successful crystal 0 71.5 214.5 286

In the monocrystalline silicon in Comparative 1 as understood from Table2 and FIG. 3 , the occurrence rate of dislocations before reaching apoint of 80 mm from the straight-body start point was 7%, which meansthat occurrence of dislocations was preventable at a high probability.However, as understood from Table 1 and FIG. 2 , the resistivity of themonocrystalline silicon was 1.0 mΩcm even at the straight-body length100% point. Thus, the monocrystalline silicon having a low resistivityof 1.0 mΩcm or less was not produced.

The monocrystalline silicon in Comparative 2 had the resistivity of 1.0mΩcm or less at a point indicating 35% of the straight-body length(hereinafter, referred to as the straight-body length 35% point) fromthe straight-body start point as understood from Table 1 and FIG. 2 .However, as understood from Table 2 and FIG. 3 . the occurrence rate ofdislocations until reaching the point of 80 mm from the straight-bodystart point was as extremely high as 87%. Accordingly, when dislocationsoccur before reaching the point of 80 mm from the straight-body startpoint, a seed crystal needs to be again immersed into the melt andpulled up, resulting in increasing the production cost.

In contrast, the resistivity of the monocrystalline silicon in Example 1was 1.0 mΩcm or less at the straight-body length 70% point from thestraight-body start point. Further, the occurrence rate of dislocationsbefore reaching 80 mm from the straight-body start point was as low as21% and the monocrystalline silicon 10 that was dislocation-free overthe entire length accounted for 43%. Thus, it was confirmed that themonocrystalline silicon having a low resistivity of 1.0 mΩcm or less wasproducible at a low cost.

Likewise, the resistivity of the monocrystalline silicon in Example 2was 1.0 mΩcm or less at the straight-body length 50% point from thestraight-body start point. Further, the occurrence rate of dislocationsbefore reaching the point of 80 mm from the straight-body start pointwas as low as 30% and the monocrystalline silicon 10 that wasdislocation-free over the entire length accounted for 40%. Thus, it wasconfirmed that the monocrystalline silicon having a low resistivity of1.0 mΩcm or less was producible at a low cost.

[2] Dopant in Form of Arsenic

The monocrystalline silicon 10 doped with arsenic was pulled up while aresistivity of the monocrystalline silicon 10 was controlled by addingarsenic as the dopant depending on a point in the straight-body lengthof the monocrystalline silicon Results are shown in Table 3 and FIG. 4 .The inner diameter of the crucible 3, the straight-body diameter of themonocrystalline silicon 10, and the rotation speed of the crucible 3were the same as those when red phosphorus was used.

TABLE 3 Comp. 3 Ex. 3 Ex. 4 Comp. 4 resistivity straight-body length 0%point 3.1 2.9 2.6 2.3 [m Ω cm] (end of shoulder) straight-body length20% point 2.8 2.6 2.34 2.07 straight-body length 40% point 2.47 2.292.05 1.82 straight-body length 60% point 2.19 2.05 1.85 1.7straight-body length 80% point 2.06 1.9 1.7 1.6 straight-body length100% point 2.01 1.83 1.683 1.6 (tail start point)

Presence or absence of occurrence of dislocations was checked in eachpoint. Results are shown in Table 4 and FIG. 5 .

TABLE 4 Comp. 3 Ex. 3 Ex. 4 Comp. 4 dislocations shoulder tostraigh-body  6%  36%  50%  87% rate 80 mm point (trial no./straigh-body 80 mm point to  0%  0%  11%  13% no.) straigh-body length20% point  0%  0%  7%  0% straigh-body length 20% to 40% point  0%  0% 5%  0% straigh-body length 40% to 60% point  0%  0%  0%  0%straigh-body length 60% to 80% point  0%  7%  0%  0% straigh-body lengthtail start point  31%  29% 2%  0% dislocation-free in  63%  29%  25%  7%entire crystal length total 100% 100% 100% 107% N shoulder tostraigh-body 1 5 22 13 number 80 mm point (trial no.) straigh-body 80 mmpoint to 0 0 5 2 straigh-body length 20% point 0 0 3 0 straigh-bodylength 20% to 40% point 0 0 2 0 straigh-body length 40% to 60% point 0 00 0 straigh-body length 60% to 80% point 0 1 0 0 straigh-body lengthtail 5 4 1 0 dislocation-free in 10 4 11 1 entire crystal length total16 14 44 15 diameter 300 mm 300 mm 300 mm 300 mm dopant arsenic arsenicarsenic arsenic crystal yield  0%  22%  44%  52% charge amount 160 160160 160 straight-body length 710 710 710 710 rate of successful crystalin  0%  30%  60%  70% length length of successful crystal 0 213 426 497

In the monocrystalline silicon in Comparative 3 as understood from Table4 and FIG. 5 , the occurrence rate of dislocations before reaching apoint of 80 mm from the straight-body start point was 6%, which meansthat occurrence of dislocations was preventable at a high probability.However, as understood from Table 3 and FIG. 4 , the resistivity was 2.0mΩcm even at the straight-body length 100% point. Thus, themonocrystalline silicon having a low resistivity of 2.0 mΩcm or less wasnot produced.

The monocrystalline silicon in Comparative 4 had the resistivity of 2.0mΩcm or less at the straight-body length 25% point from thestraight-body start point as understood from Table 3 and FIG. 4 .However, as understood from Table 4 and FIG. 5 . the occurrence rate ofdislocations until reaching the point of 80 mm from the straight-bodystart point was as extremely high as 87%. Accordingly, when dislocationsoccur before reaching the point of 80 mm from the straight-body startpoint, a seed crystal needs to be again immersed into the melt andpulled up, resulting in increasing the production cost.

In contrast, the resistivity of the monocrystalline silicon in Example 3was 2.0 mΩcm or less at the straight-body length 65% point from thestraight-body start point. Further, the occurrence rate of dislocationsbefore reaching the point of 80 mm from the straight-body start pointwas as low as 36% and the monocrystalline silicon 10 that wasdislocation-free over the entire length accounted for 29%. Thus, it wasconfirmed that the monocrystalline silicon having a low resistivity of2.0 mΩcm or less was producible at a low cost.

Likewise, the resistivity of the monocrystalline silicon in Example 4was able to be made 2.0 mΩcm or less at the straight-body length 45%point from the straight-body start point. Further, the occurrence rateof dislocations before reaching the point of 80 mm from thestraight-body start point was as low as 50% and the monocrystallinesilicon 10 that was dislocation-free over the entire length accountedfor 25%. Thus, it was confirmed that the monocrystalline silicon havinga low resistivity of 2.0 mΩcm or less was producible at a low cost.

From the foregoing, when the monocrystalline silicon was pulled upthrough the Czochralski process from the silicon melt containing redphosphorus as the dopant, the resistivity of the monocrystalline siliconat the straight-body start point was controlled to fall within a rangefrom 1.20 mΩcm to 1.35 mΩcm and was subsequently sequentially decreased,so that the resistivity of a part of the monocrystalline silicon fellwithin a range from 0.7 mΩcm to 1.0 mΩcm and occurrence of dislocationsof the monocrystalline silicon was prevented.

Likewise, when the monocrystalline silicon was pulled up throughCzochralski process from the silicon melt containing arsenic as thedopant, the resistivity of the monocrystalline silicon at thestraight-body start point was controlled to fall within a range from2.50 mΩcm to 2.90 mΩcm and was subsequently sequentially decreased, sothat the resistivity of a part of the monocrystalline silicon became ina range from 1.6 mΩcm to 2.0 mΩcm and occurrence of dislocations of themonocrystalline silicon was prevented.

1. A production method of a monocrystalline silicon, comprising: growingthe monocrystalline silicon having a straight-body diameter in a rangefrom 301 mm to 330 mm that is pulled up through a Czochralski processfrom a silicon melt comprising a dopant in a form of arsenic, an innerdiameter of a quartz crucible that stores the silicon melt being 1.7 to2.0 times as large as the straight-body diameter; pulling up themonocrystalline silicon while rotating the quartz crucible at a rotationspeed ranging from 9 rpm to 30 rpm at a start of formation of thestraight-body; changing the rotation speed of the quartz crucible to arange from 0.1 rpm to 7 rpm in a case that the straight-body of themonocrystalline silicon is pulled up from a straight-body start point ofthe monocrystalline silicon to reach a range from 50 mm to 200 mm;controlling a resistivity of the monocrystalline silicon at thestraight-body start point to fall within a range from 2.50 mΩcm to 2.90mΩcm, and subsequently sequentially decreasing the resistivity of themonocrystalline silicon to fall within a range from 1.6 mΩcm to 2.0 mΩcmat a part of the monocrystalline silicon.
 2. The method of claim 1,further comprising: pulling up the monocrystalline silicon whilerotating the quartz crucible at a rotation speed ranging from 16 rpm to30 rpm at a start of formation of a shoulder, and lowering the rotationspeed of the quartz crucible to fall within a range from 4 rpm to 12 rpmin a case that a diameter of the shoulder is equal to or more than ahalf of the straight-body diameter.